From the drug perspective, penicillins themselves are not common allergens; it is the impurities (penicillin thiazoles, penicillin enolates, penicillin amines and other polymers) produced during the synthesis and production of penicillins that cause allergy in patients. According to current research, penicillin allergic reactions are similar to other drug allergic reactions in that they are the result of drug semi-antigens entering the body and combining with tissue proteins in the body to become complete antigens, thus stimulating the body to produce an immune response. What is the allergenic substance of penicillin allergic reaction? In the study of penicillin allergic reaction, it was found that penicillin molecules in pH 7.5 aqueous solution quickly rearranged into penicillin enolic acid, which then decomposed into penicillin thiazolic acid. This penicillin thiazolic acid can bind with gamma-globulin and albumin in human tissues to form penicillin thiazole protein. This penicillin thiazole protein is the main sensitizing substance that causes penicillin allergic reactions. Penicillin thiazole antibodies can be measured in the serum of patients who have just had an allergic reaction, which also confirms the important role of penicillin thiazole protein in the formation of allergic reactions. Penicillin thiazole protein is not only formed in human body, but also can be formed in the process of penicillin production or storage, especially when the purified and refined penicillin solution itself may contain penicillin thiazole protein or contain more impurities, injecting this penicillin solution, it may directly cause penicillin allergic reaction, and even anaphylaxis occurs.